The biological clock may be ticking for thousands of women. But the dilemma over the best age to start a family has finally been solved: women should aim for 34.

The biological clock may be ticking for thousands of women. But the dilemma over the best age to start a family has finally been solved: women should aim for 34.

A study of 3,000 young mothers has found that when it comes to maternal health this is the best age for women to have their first baby - suggesting that women who put their families on hold in order to establish their careers do not lose out.

Academics looked at the link between health problems of around 3,000 women, and their age at their first delivery. Women who first gave birth around puberty developed more health problems. The longer the first birth was delayed, up to the age of 34, the fewer the health problems now. After that age, they rose again. Health benefits started at the age of 22, peaking at 34.

"At any age, a woman who had her first child at 34 is likely to be, in health terms, 14 years younger than a woman who gave birth at 18," said Professor John Mirowsky, who led the research published by the Health and Social Behaviour Journal.

His findings have been questioned, however. Melanie Every, a spokeswoman for the Royal College of Midwifery, argued that the key factor was social background, rather than age.

"Career women who have delayed having a family have higher incomes, better education, better diets and better housing conditions, and these factors are important," she said. "A younger woman will be better from a purely physical fitness view, but if you look at social security, finance and the child's development and health, being a little older and having more life expectancy can be helpful."

Cecilia Pyper, a senior research fellow at the Department of Public Health at Oxford University and a fertility expert, warned that women must bear in mind that they become less fertile after the age of 35.

"Fertility is declining from then, and for women who are just starting a family, it is pretty tight," she said. "Breastfeeding suppresses ovulation. A woman who has her first child at 34 will not be having her second until she is 37 or 38.

"Women who want a family should not be targeting the age of 34 for the first time to get pregnant. I think a lot of women are looking at the age of 30, so if they run into trouble they can still have IVF and a second child."

Professor Mirowsky acknowledges this point: "Even compared with the mid-20s, the advantages increase up to the age of 34. But the longer you wait, the better, up to a point. When you reach that point, the reproductive system is declining, there is the risk of chronic disease, and you cannot put it off. It is all about trade-offs."

More and more women are choosing to have children later. While the average age for a first birth in the UK is 29, the number of women aged between 30 and 34 giving birth has increased steadily in the past 10 years. At 94.9 births per 1,000 in 2003, this age group is only marginally behind the 25 to 29 age group, at 95.8 as the most popular age for giving birth.

The number of women giving birth up to the age of 40 and over has also seen a steady rise, one of the reasons for the research, funded by the US National Institute on Ageing and the National Institute of Mental Health.

Professor Mirowsky added: "This trend has led some people to feel alarm about implications for the health of mothers and infants.

"The results of this study suggest there is no cause for that alarm. The social and economic benefits of delaying parenthood more than compensate for the ageing reproductive system."

'I look at younger mums and I wonder how they will cope'

By Linda Jones

Allison Whordley from Cannock, Staffordshire, found that a few years of experience were a real help when, at the age of 34, she gave birth to her first child, Summer.

"Being that bit older has meant I am more in tune with what Summer needs and wants. You are at a stage in your life where you can be more relaxed about it and appreciate how precious children are. There's also the peace of mind of having finances sorted - by having a good few years of working behind you - and not having to worry about where cash is going to come from if you have to take time away from work early on. I had a very secure job at an estate agents.

"There do seem to be a lot of very much younger mums around these days. When I see them with their pushchairs I wonder how they are going to cope. I won't ever be wistfully thinking of the times I could be having if I hadn't had Summer."